Municipal waste has traditionally been disposed of in landfill sites. However, the environmental hazards of doing so are becoming a major concern and therefore an effort has been made in recent years to develop waste-treatment processes that reduce the volume of the waste material and the amount of potentially environmentally hazardous constituents in the treated material.
EP1896774 discloses the treatment of such municipal waste in a two step process. Firstly, the waste is gasified in a gasification unit. Gasification, while being moderately successful in combusting the majority of waste, nevertheless produces a gas that contains uncombusted particulates, low volatility tarry species, airborne compounds and a solid non-airborne char.
The gas that results from the gasification of waste (termed an ‘offgas’) can be used in a gas turbine, but the airborne particulates and tarry hydrocarbon molecules have a tendency to clog the turbine or engine. EP1896774 therefore discloses a plasma treatment of the off-gas and the solid non-airborne char in a plasma treatment unit. This extracts any remaining organic species from the char, which it then vitrifies, and cracks any airborne organic species into carbon monoxide and hydrogen for use in a gas engine.
Gas engines are sensitive to the homogeneity of the syngas feedstock. Accordingly, the process disclosed in EP1896774 is preferably used to treat homogenised organic waste of constant calorific value (CV). Indeed, the process disclosed in EP1896774 is optimised for the treatment of Refuse Derived Fuel (RDF) and Solid Recovered Fuel (SRF), although treatment of any waste is contemplated.
Hazardous wastes come in many different forms, for example, tyres, paints and soil. Hazardous wastes have different calorific content and volatilities and therefore such wastes need to be recycled individually using specialist treatment methods.
Accordingly, there is a desire for a process that will overcome, or at least mitigate, some or all of the problems associated with the methods of the prior art or at least a useful or optimised alternative.